It is known that in radial tires the reinforcing material placed at small angles with the equatorial plane on belt package enhances the performance of the radial tire especially at high speeds.
Using hybrid cords as cap ply reinforcement by being wound on the belt package spirally as strips has been used for many years by several companies in order to improve high speed durability and handling performance in pneumatic radial tires. The said hybrid cord strips are obtained by cutting calendered (rubberized) cord fabric in strips or rubberizing parallel single cords in a certain width during extrusion process.
Hybrid cords are composed of at least two yarns (plies) having different properties (such as elastic modulus). For example, aramide-nylon hybrid cords are commonly used as cap ply reinforcement strip in pneumatic tires. The hybrid cords composed of two different yarns generally have two different tangent modulus zones. The initial low modulus zone is required for avoiding tight cord formations in geometric expansions during preparation and vulcanization of green tire and preventing the tight cord formations which could have cutting effect in the rubber. The high modulus zone is needed to prevent tire growth generated by the steel belt Package due to centrifugal force at high speeds. The tire growth causes the belt edge separation and cracks formed at the bottom of the tread grooves.